Two cerebral metabolic patterns revealed by positron emission tomography (PET) are characteristic of Alzheimer disease (AD) and were identified using regional covariance analysis of resting state data. These patterns distinguished AD patients from patients with frontotemporal dementia and were correlated with specific cognitive deficits in the AD group. Among AD patients, dementia was related to greater impairment on tests of visuospatial function. AD patients with a family history of dementia showed greater rCMRglc deficits in frontal association regions. Further, a unique subgroup of AD patients with early prominent visual disturbances showed cerebral hypometabolism in parieto-occipital and calcarine cortices with relative sparing of paralimbic regions compared to typical AD patients. This pattern remained after atrophy correction. In this subgroup, postmortem pathology showed a distribution of senile plaques and neurofibrillary tangles consistent with the pattern of metabolic deficits. Studies of visuospatial attention in healthy subjects performing a visual search task showed incremental slowing of reaction time with more attentional distractors. Increasing distraction was accompanied by activation of a region in right prefrontal cortex thought to participate in attentional processing. Despite poor figural reproduction across multiple learning trials, AD patients with mild to severe dementia showed some acquisition of visual material during figural reproduction that predicted recognition performance and was unrelated to degree of visuospatial impairment. Longitudinal studies of AD patients show heterogeneity in rates of cognitive decline and of visual attentional processing.Two families of textures were passively presented to healthy volunteers undergoing PET: Random textures in which black and white checks were arranged in a random fashion, and Even textures in which the checks were ordered to produce extended contours and rectangular blocks at multiple spatial scales. In young subjects, relative to random texture stimulation, presentation of Even textures resulted in increased blood flow in striate and extrastriate cortices, hippocampus and prefrontal cortex. In old subjects, relative to Random stimulation, Even stimulation increased flow in extrastriate and inferior frontal cortices. The extrastriate and frontal regions that were activated in the old subjects were not activated in the young subjects, suggesting a reallocation of cortical resources during visual perception with age.Cerebral blood flow in control and AD patients changed in visual brain areas in response to increasing frequency of visually presented flashes. In striate cortex, a peak flow response was found at 8 Hz, whereas in extrastriate visual cortex, flow increased with frequency to 16 Hz. Flow responses were abnormal in AD patients, in relation to dementia severity, but in some regions administration of the anticholinesterase drug, physostigmine, tended to normalize the AD responses. In the thalamus of AD patients, changes in flow after administration of the cholinergic blocker scopolamine with physostigmine indicated that physostigmine acted via cholinergic M1 receptors. - Brain, Alzheimer disease, Aging, Positron emission tomography, Cognitive function, Activation, Humans - Human Subjects